This invention relates to silyl ketene acetals which are stabilized against oxidation with ambient oxygen. More specifically, this invention relates to silyl ketene acetals in which a minor portion of a phenolic compound has been added as an oxidation inhibitor.
The first reference to preparation of silyl ketene acetals (SKA) was in the late-1950's by Petrov et al., J. Gen. Chem. (USSR), 29(1959), pp. 2896-2899. Silyl ketene acetals are characterized by the backbone structure, ##STR1## These organosilane intermediates are of interest because of the ability to further react the SKA's to other intermediates which would be difficult to synthesize by other means. A very recent application is the use of SKA's as acrylate polymerization initiators. This concept known as Group Transfer Polymerization (GTP) was developed by DuPont and is disclosed in three recent U.S. patents--U.S. Pat. No. 4,414,372, Farnham et al., issued Nov. 8, 1983; U.S. Pat. No. 4,417,034, Webster, issued Nov. 22, 1983; and U.S. Pat. No. 4,508,880, Webster, issued Apr. 2, 1985.
Rutbottom and Marreno, Syn. Comm., 11(6) (1981), pg. 505-511, discloses that meta-chloroperbenzoic acid (MCPBA) oxidizes SKA's to form alpha-hydroxy esters. Tamao and Maeda, Tetrahedron Letter, 27: 1 (1986), pp. 65-68, report that vinyl alkoxysilanes undergo a similar oxidative rearrangement with MCPBA.
Phenolic compounds, primarily phenolic compounds with a hindered structure, are known to be polymerization inhibitors for vinylic materials such as acrylates and methacrylates. Inhibitors such as 4-methoxyphenol, 2,6-di-t-butyl-4-methylphenol, and 2,4-di-methyl-6-t-butylphenol are known to be effective in preventing radical chain polymerization of alpha,beta-unsaturated esters. 2,4-di-methyl-6-t-butylphenol, also known as butylated hydroxytoluene or BHT, is also known as an antioxidant for food, animal and vegetable oils, synthetic rubber, plastics, and soaps.
None of the above references demonstrate or suggest the mixture of an SKA and a phenolic compound as disclosed by the instant invention.
The objective of the instant invention is to provide a silyl ketene material with a significantly reduced susceptibility toward oxidation on contact with ambient air.